Dr. Noriko Hasebe at Division of Terrestrial Environmental Studies revealed environmental regime shift occurred about 2500 years ago, and published the result in Catena, volume 159.

Detailed geochronological study on Lake Yogo sediment core revealed the environmental regime shift occurred 2500 years ago probably caused by the agricultural use and vegetation change in the catchment.

Journal title: Catena, 159, 171-175
Title: Environmental regime change at around 500BCE found in sediment cores from Lake Yogo, Japan: Possible impact of agricultural use
Authors: Hasebe, N., Hayashi, H., Ito, K., Ogata, M., Shimada, T., Itono, T.